1. Field of the Invention
The present invention relates to a sealing structure for sealing a gap around a combustor liner. More specifically, the present invention relates to a sealing structure for a sealing gap around a combustor liner for a gas turbine to be used as, for example, an aircraft engine.
2. Description of the Related Art
Development of ceramic materials, such as CMCs (ceramics matrix composites), superior in heat resistance in comparison to conventional metallic materials has made progress in recent years, and studies have been made to use such ceramic materials for forming combustor liners. In the case of the conventional combustor liner made of a metallic material having low heat resistance, it is difficult to significantly reduce the amount of cooling air for cooling the combustor liner. On the other hand, when a combustor liner made of a ceramic material having high heat resistance is used as a combustor, it is possible to reduce the amount of cooling air, to improve the thermal efficiency of the combustor, and to reduce mission of nitrogen oxides by using surplus cooling air for producing a lean combustion.
However, since ceramic materials, in general, are brittle and have linear expansion coefficients smaller than those of metallic materials, the difference in thermal expansion between a combustor liner of a ceramic material and structures of metallic materials surrounding the combustor liner is large while the combustor operates under the condition of high temperature. Thus, a sealing structure sealing gaps between the combustor liner of a ceramic material and the associated surrounding structures of metallic materials must be capable of absorbing the difference in thermal expansion.
Referring to FIGS. 13A and 13B, a conventional sealing structure for a combustor liner proposed in Japanese Patent No. 2852110 includes a plate spring 103 sealing a gap between a premixer 101 and a liner 102, and capable of elastically deforming to absorb the displacement of the liner 102 relative to the premixer 101. A sealing structure disclosed in JP8-285284A includes a plate spring sealing the gap between a liner and a transition piece.
Thus, most conventional sealing structures for sealing gaps around combustor liners use plate springs to absorb the difference in thermal expansion between the combustor liner and the associated surrounding structure. Such a plate spring used for absorbing the difference in thermal expansion must have a low rigidity so that an excessive stress may not be induced in the plate spring and the liner may not be excessively loaded, and hence the plate spring must have a big length.
The difference in thermal expansion coefficient between a CMC and a metal is large, and a plate spring used for sealing the gap between a liner of a CMC and the associated surrounding structure of a metal needs to have a long length and needs a large space for installation. Such requisite conditions for using a combustor liner of a CMC is very disadvantageous in applying the combustor liner to a gas turbine serving as an aircraft engine in which reduction of weight and space for installation is very important.
The dimensions of a large, long plate spring used for sealing the gap around the combustor liner of a CMC change greatly when the plate spring is heated and, consequently, the plate spring is unable to maintain a stable sealing function at high temperatures.
The plate spring of the foregoing conventional sealing structure is placed in direct contact with the combustor liner. Therefore, when the plate spring is used for sealing the gaps around a combustor liner of a CMC that is heated at higher temperatures in comparison to a combustor liner of a metal, it is possible that the elasticity of the plate spring is lost due to creep and the sealing function of the plate spring is deteriorated in a short period of operation.